When did they drop in quality? If I'm looking used anyway its something to bear in mind.
They started using Taiwanese bridges and such around 2003/2004. In 2008, they briefly went to a Chinese made molded case, instead of U.S. made SKB. That was a piece of crap, and they started using decent quality G&G cases with form fitted interiors and eight metal feet in about 2010. In about 2016, they did another major cheapening, and the cases went way downhill. The G&G cases no longer used form fitted padding, went to four metal feet only, a smaller interior pocket, cheesier case hardware, and thinner basic case materials (wood, vinyl, padding, interiors). Whether G&G simply can't build a high quality case any more, or if G&L just started ordering cheaper options from G&G, I do not know.
At this time, they started using the two-way truss rod with a welded nut, which, if it breaks, means the whole neck is trash, and can't be repaired...and I've read of many breaking...but they're easier for the factory to install, because they're purchased already assembled, and just drop in to a straight-routed channel. They started using stiffening rods in their necks, which when employed in mass production, pretty much just means that the company isn't spending the money, taking the time, or employing the skill it takes to selects and handle lumber properly, and is losing a lot of money on warranty neck replacements. (FWIW, I have also heard of plenty of the post-2015 necks going bad, even with stiffening rods and two-way truss rods.)
That's also about when they stopped using Schaller tuners, and started using Taiwanese ones. The pickup baseplates went from copper to a cheaper metal around the same time. Now, they've stopped including hard cases at all, unless you get a Custom Shop instrument for $3,000 + (and even then, you still get a low to mediocre quality G&G hard case made with cheap materials and parts).
There's also the argument that as time has marched on, the last generation of American craftsmen who actually knew what the hell they were doing with hand labor has aged out or moved on to bigger and/or better guitar companies.
Some of this is industry wide, and some of it is just happening at G&L.
In short, the best quality period is before 2003, though there can still be very good ones after that. But I wouldn't touch anything after 2015, unless I planned on spending the dough to at the very least upgrade the tuners and the hard case. And I would never trust the neck – always would be afraid of it maxing out or the welded nut snapping off, as I use heavy strings.
As another way of looking at it, I probably have about 100 G&Ls. Two of these are post 2015 (and I am really not fond of one of these). Seven or eight are post 2002. So, out of the large collection, only about 10 percent are post 2002.
As yet another way of looking at it, in the past 20 years, the quality gap between the U.S. and the Tribute models has narrowed significantly, almost entirely by way of the U.S. models getting worse. Concurrently, the prices of these U.S. models have more than doubled in this time period. Point being, I would really consider a Tribute that you spruce up a bit, over a late model U.S. one. Yes, they're cheaper for a reason...but the differences between them and the new U.S. models usually do not warrant the difference in price. On the used market, things change a bit, and the price difference might be more worth it.